Advances in the safe storage of micropropagated woody plants at low temperature

The conservation of micropropagated plants (also referred as "slow growth storage") enables the maintenance in vitro of shoot cultures in aseptic conditions by reducing markedly the frequency of periodic subculturing (from a few months to one year or more, depending on the species), without affecting the viability and regrowth potential of shoots. The technique is a tool of strategic importance for commercial micropropagation laboratories, which need today to counteract competition by broadening the offer of species and cultivars, and achieving in general a better organization of their high-quality production. Indeed, the conservation at low temperature allows a significant extension of the interval between subcultures, thus reducing the costs of stock culture maintenance, as well as the risk of contamination during shoot manipulation. The most widely used approach for slow growth storage is based on coupling the application of low temperature (generally, 2-5°C for temperate woody species) with culture in darkness. Low temperature and darkness (or low light intensity) have physiological consequences, such as the reduction of respiration, water loss, wilting, and ethylene production, which allow safe conservation of shoot cultures. However, other factors (i.e., the characteristics of explants and the quality of shoot cultures, the genotype, the medium formulation and the characteristics of containers) play an important role in achieving the maximum time of conservation of shoots that, when moved back to standard culture conditions, should regrow quickly and resume their original proliferation rate. All these factors are critically analyzed in this report. Moreover, information is provided on the conservation at low temperature of alginate-encapsulated buds from in vitro culture (synthetic seeds). © ISHS 2013.